To connect multiple electrode layers of a three-dimensional memory device to a control circuit, a staircase-shaped contact structure of the multiple electrode layers has been proposed. After patterning a portion of the stacked body including the multiple electrode layers (or sacrificial layers to be replaced with the electrode layers) and the multiple insulating layers into a staircase configuration, an insulating layer is formed on the staircase portion. Contact portions pierce the insulating layer and reach the staircase portion. Also, it has also been proposed to form a slit by collectively etching the stacked body and the insulating layer on the staircase portion for the processes or for electrical isolation.